Hydraulic brake wheel cylinder



Aug. 20, 1940. E. R. PIERCE El AL 2,212,245

HYDRAULIC BRAKE WHEEL CYLINDER Filed May 12, 1958 2 Sheets-Sheet lZmnentors 5 93 9 12766 & BB 9105a xezms u/ attorn g Aug. 20, F340. E. R.PlERcE ET AL 2,212,246

HYDRAULIC BRAKE WHEEL CYLINDER Filed May 12, 1938 2 Sheets-Sheet 2 55 47[03 Q7 47 I I Gttornegs Patented Aug. '20, 1940 UNITED STATES nrmuwucBRAKE WHEEL crnmnsn Earl R. Pierce and Gilbert K. Hause, Dayton,

Ohio, assignors to General Motors Corporation, Detroit, Mich, acorporation of Delaware Application May 12, 1938, Serial No. 207,616

Claims.

This invention relates to hydraulic motors and has been designedespecially to serve as a wheel cylinder in a hydraulic brake system.

An object of the invention is to so make a 5 wheel cylinder that animproved seal is obtained to prevent leakage.

Another and more specific object is to prevent leakage by the use of asealing diaphragm of flexible incompressible material.

Still another objectis to provide an exceedingly simple construction forsecuring such a seal or diaphragm in place.

Other objects such as efllciency in operation and economy in manufacturewill be understood from the following description.

In the drawings:

Figure 1 is a vertical section through one embodiment of the invention.

Figure 2 is a perspective of a detail.

Figure 3 is a view like Figure 1 of a. second form of the invention.

Figure 4 is a perspective of a part used in Figure Figure 5 is avertical section through a third 25 embodiment.

Figure 6 is a perspective of several parts used in the third form of theinvention, the parts being shown in disassembled relation.

Figure 7 is a sectional view of still another embodiment.

Referring to Figures 1 and 2, numeral II represents a conventional brakedrum. such a drum as is usually mounted on vehicle wheels. As iscustomary the drum is closed by a cover plate l3, this plate beingcarried by the dead axle or other non-rotating part. The drawing showstwo shoes I5 and I! which are suitably assembled to frictionally engagethe drum, there being provided suitable lining material 19. Theanchorage of the shoes to the backing plate'may be conventional and isnot shown. Normally the shoes are retracted from engagement with thedrum by a spring 20 terminally connected to the shoes as shown. 3

The wheel cylinder is formed with a face portion 2| having apertures forthe passage of fastening means 23 connected to the cover plate i3.- Thecylinder consists of two parts 25 and 21. Part 25 has an enlargeddiameter portion 29 and a reduced end 3|. A piston 33 slides through thereduced end 3|. Part 21 is threaded at 35 into the enlarged part 22 andits inner diameter corresponds with the inner diameter of part 31.Reciprocable within part 21 is a second piston 31. The pistons 33 and 31have axial recesses 39 into which freely project the ends of threadedstems 4|,the other end of the stems being forked to engage the ends ofthe webs 43 of the shoes. Cup shaped members 45 overlie the ends of thepistons. when the pistons are retracted the bot- 5 toms of the cups l5engage the ends of the cylinder parts 25 and 21 as well as the piston asshown by Figure 1. The walls of these cups 45 embrace the ends of thecylinder as shown. Nuts 41 are threaded on the stem. Rotation of thenuts serves to reciprocate the stems to determine the release positionof the shoes and to correct the wear of the friction linings IS.

The pistons have opposed convex faces 5| engaged by diaphragms 53 ofrubber and other like material which is incompressible but elastic. Onediaphragm preferably engages the shoulder 55 between the two diameterparts of member 25. The marginal wall of the other diaphragm lies flatagainst the end of part 21. Since the diaphragms are bowed to thepositions shown when the brake is released they are flattened in the actof spreading the shoes thereby tending to crowd the mass of the rubberand so to increase its efficiency. With such a sealing diaphragm it isnot necessary to use parts of the wheel cylinder to grip the rubber atits periphery. A somewhat lighter pressure at the marginal wall issumcient, this pressure being great enough to prevent leakage when thebrake is released and this pressure adapted to be supplemented by thefluid pressure when the brakes are applied. To that end there are usedcup shaped members 51 each having a radially extending marginal portion59, an axially directed side wall 51 and a bottom portion 53 the latterbeing apertured as at 55 for the passage of the hydraulic fluid. Themarginal portions 59 engage the rubber seals as shown. Between the twocups is a spider expander 51 (Figure 2). It has a central portion 65 andspring fingers 1i bent alternately in opposite directions, the fingershaving axially directed ends 13. The alternate spring fingers engage theends of the axial portions of the cups 51. The spider is placed betweenthe cups 51 and its spring fingers are prestressed in the process ofassembly and thereby the cups are pressed apart exerting a yieldingpressure on the marginal portions of the rubber seals to preventleakage. In use of the brake the movable column of fluid enters thecylinder through opening 15. The fluid under pressure pushes the bowedrubber diaphragms. the diaphragms being flattened push the pistons 33and 31 and apply the shoes to the drum. At the same time the fluid underpressure supplements the spring pressure on the marginal walls of thediaphragms and holds the diaphragms firmly against their seats.

In the second form 01' the invention shown by Figures 3 and 4 similarparts are given similar reference characters. The diflerence betweenFigure 3 and Figure 1 relates solely to the parts between the twodiaphragms. There are used in this form stamped members 'll angular incross section having radial flanges l9 engaging the marginal wall of therubber seals and axially directed flanges 8i. Between the opposed endsof the axial flanges ii are spring plates '3.

These plates are bowed into conical form. They are arranged in opposedrelation contacting with each other at their outer edges adjacent thecylinder wall and are prestressed to engage the opposing edges of parts8 l The prestressed condition of these springs is sufllclent to hold therubber diaphragms sealed when the brake is released and the fluid underpressure returns from the wheel cylinder. When the brake is applied thefluid under pressure not only moves the shoes into engagement with thedrum but exerts pressure upon the marginal walls of the rubber diaphragmas before described.

In Figure also the only diflerence is in the parts located between therubber diaphragms.

In this form numeral 81. is a ring having a radial flange 89 for contactwith the outer margin of the rubber seal and an axial flange 9| spacedfrom the cylinder wall and extending toward the center of the cylinder.A second ring 93 has an axial flange 95 in parallel with and in contactwith the cylinder wall. A radial flange 91 is in contact with the secondrubber diaphragm and a short axial flange 99 radially spaced from theflange 95 extends toward the center of the cylinder. A bowed springplate Ill is prestressed to engage along its outer margin the flange 95and near its inner margin it is in contact with flange 8i. This springplate is prestressed so that the margin of the rubber is held in antleak relation with the cylinder when the brake is released. When the'brake is applied, fluid pressure flattens the diaphragms andsupplements the seal. a

In Figure 7 between the rubber diaphragms there are dome-shaped springcups I03. The cups are assembled with the marginal radial flanges I05seated against the marginal walls of the rubber diaphragms and withtheir domes in contact. When the end portion 21 is threaded into part 25the domes are flattened with the result that a spring load istransmitted from the spring cups to the marginal wall of the rubberdiaphragms and leakage is thereby prevented. The dome part of the cupremains in spaced relation from the dome portion of the rubber seal,

the cup being apertured for the passage of the hydraulic fluid. The cupsact as high rate springs and serve to accommodate any set which therubber diaphragm may assume in service.

We claim: a

l. A hydraulic motor comprising a cylinder having reduced ends forminginternal shoulders, diaphragms of flexible incompressible materialperipherally engaging said shoulders, pistons reciprocable within saidends in response to hydraulic pressure applied between and acting tomove said diaphragms, bowed spring means between said diaphragms andoperable to yieldingly urge their marginal portions against saidshoulders, "together with rings having radial flanges engaging saidmarginal portions oi the diaphragms and opposed axial flanges,saidspring means engaging said axial flanges.

2. A hydraulic motor comprising a cylinder having reduced ends forminginternal shoulders, diaphragms oi. flexible incompressible materialperipherally engaging said shoulders, pistons reciprocable within saidends in response to hydraulic pressure applied between and acting tomove said diaphragms, bowed spring means between said diaphragms andoperable to yieldingly urge their marginal portions against saidshoulders, together with angular rings having radial flanges engagingthe marginal portion of said diaphragms, opposed axial flanges and anapertured wall connecting the axial flange of each ring.

3. A hydraulic motor comprising a cylinder having reduced ends forminginternal shoulders, diaphragms of flexible incompressible materialperipherally engaging said shoulders, pistons reciprocable within saidends-in response to hydraulic pressure applied between and acting tomove said diaphragms, bowed spring means between Said diaphragms andoperable to yieldingly urge their marginal portions against saidshoulders, together with angular rings having radial flanges engagingthe marginal portions of said diaphragms. and having. opposed axialflanges, said spring means being a spring plate with oppositely bentspring tongues engaging the axial flanges of said rings.

4. A hydraulic motor comprising a cylinder having reduced ends forminginternal shoulders, diaphragms of flexible incompressible materialperipherally engaging said shoulders, pistons reciprocable within saidends in response to bydraulic pressure applied between and'acting tomove said diaphragms, bowed spring means between said diaphragms andoperable to yieldlngly urge their marginal portions against saidshoulders, together withangular rings having radial flanges and engagingsaid diaphragms and opposed axial flanges. said spring means comprisingopposed bowed or conically preformed annular discs peripherally incontact with each other and engaging under stress said axial flanges.

5. A hydraulic motor comprising a cylinder having reduced ends forminginternal shoulders, diaphragms of flexible incompressible materialperipherally engaging said shoulders, pistons reclprocable within saidends in response to bydraulic pressure applied between and acting toGILBERT K. muse.

